This part specifies how various signals relate to the available ports of the 8520. This information enables the programmer to relate the port addresses to the outside-world items (or internal control signals) which are to be affected. This part is primarily for the use of the systems programmer and should generally not be used by applications programmers. Systems software normally is configured to handle the setting of particular signals, no matter how the physical connections may change. Warning: -------- In a multitasking operating system, many different tasks may be competing for the use of the system resources. Applications programmers should follow the established rules for resource access in order to assure compatibility of their software with the system. CIA-A Address BFEr01 data bits 7-0 (A12*) (INT2) PA7..game port 1, pin 6 (fire button*) PA6..game port 0, pin 6 (fire button*) PA5.. RDY* disk ready* PA4.. TK0* disk track 00* PA3.. WPRO* write protect* PA2.. CHNG* disk change* PA1..LED* led light (0=bright) PA0..OVL memory overlay bit SP... KDAT keyboard data CNT.. KCLK keyboard clock PB7..P7 data 7 PB6..P6 data 6 PB5..P5 data 5 Centronics parallel interface PB4..P4 data 4 data PB3..P3 data 3 PB2..P2 data 2 PB1..P1 data 1 PB0..P0 data 0 PC... drdy* Centronics control F.... ack* CIA-B Address BFDr00 data bits 15-8 (A13*) (INT6) PA7..com line DTR* , driven output PA6..com line RTS* , driven output PA5..com line carrier detect* PA4..com line CTS* PA3..com line DSR* PA2.. SEL centronics control PA1.. POUT paper out ---+ PA0.. BUSY busy ---+ | | | SP... BUSY commodore -+ | CNT.. POUT commodore ---+ PB7.. MTR* motor PB6.. SEL3* select external 3rd drive PB5.. SEL2* select external 2nd drive PB4.. SEL1* select external 1st drive PB3.. SEL0* select internal drive PB2.. SIDE* side select* PB1.. DIR direction PB0.. STEP* step* (3.0 milliseconds minimum) PC...not used F.... INDEX* disk index* 8520_timing.asm
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